When we want to compare two things, we use the comparative form. For example, "She is less experienced than him." Here, we are comparing the level of experience between two people, and "less" is used to show a lower degree of experience in comparison to the other person.
On the other hand, when we want to compare more than two things, we use the superlative form. For example, "He is the least talented among all the contestants." In this sentence, we are comparing the talent level of multiple contestants, and "least" is used to indicate the lowest degree of talent in comparison to the others.
So, whether we are comparing two things or more than two things, "less" is used for the comparative form and "least" is used for the superlative form when it comes to describing a lower degree of something.